In a mobile communication system, due to the time-varying characteristics of a wireless fading channel, a communication process has a lot of uncertainty. On the one hand, in order to improve the throughput of the system, high-order modulation with a high transmission rate and less redundant error correction codes are used for communication. In this case, the throughput of the system is indeed improved greatly when a signal-to-noise ratio of the wireless fading channel is ideal. However, when the channel is in deep fading, it cannot be guaranteed that the communication is reliable and stable. On the other hand, in order to guarantee the reliability of communication, low-order modulation with a low transmission rate and large redundant error correction codes are used for communication. That is, when the channel is in deep fading, it can be guaranteed that the communication is reliable and stable. However, when the signal-to-noise ratio of the channel is high, improvement of the throughput of the system is restricted due to a low transmission rate, which results in a waste of resources. In the early development of the mobile communication technology, in order to deal with the time-varying characteristics of the wireless fading channel, people can only increase the transmission power of the transmitter and use a low-order large-redundancy modulation and coding scheme to ensure the communication quality of the system when the channel is in deep fading, and there is no time to consider how to improve the throughput of the system. With the progress of the technical level, there is a technology that adaptively adjusts its transmission power, modulation and coding scheme and frame length of data according to a channel state to overcome the time-varying characteristics of the channel, so as to obtain the best communication effect. This technology is called an adaptive modulation and coding technology, which belongs to the most typical link adaptation technology.
In the Long Term Evolution (LTE) system, in order to implement a downlink adaptive modulation and coding technology, it needs to transmit the control signaling including Channel State Information (CSI) in the uplink. The CSI includes a Channel Quality Indication (CQI), a Pre-coding Matrix Indicator (PMI), and a Rank Indicator (RI). The CSI reflects the state of the downlink physical channel. The base station performs downlink scheduling as well as modulation and coding of data using the CSI.
The base station performs scheduling using the CSI reported by the terminal and determines a downlink Modulation and Coding Scheme (MCS) index and resource allocation information. Specifically, the Rel-8 LTE protocol defines a modulation and Transport Block Size (TBS) index table for a Physical Downlink Shared Channel (PDSCH), which may be referred to as a downlink MCS table hereinafter. The table has a total of 32 levels. Each level basically corresponds to a MCS index, and each MCS index essentially corresponds to a MCS. Further, the resource allocation information gives a Number Physical Resource Block (NPRB) which need to be occupied by the downlink transmission. The LTE standard also provides a TBS table. After the MCS index and the NPRB are given, the TBS can be acquired according to the table. With these modulation and coding parameters (MCS/NPRB/TBS), the base station can carry out modulation and coding of the downlink data for downlink transmission.
After the terminal receives the data of the downlink transmission, it needs to obtain the MCS index and the resource allocation information of the downlink transmission for data processing. Further, the base station transmits the MCS index and the resource allocation information through Downlink Control Information (DCI). The base station scrambles Cyclic Redundancy Check (CRC) bits corresponding to the downlink control information using a specific Radio Network Temporary Identity (RNTI), and transmits the downlink control information in a specific DCI format through a Physical Downlink Control Channel (PDCCH). The terminal carries out blind detection in a Common Search Space (CSS) and a User Equipment (UE) specific Search Space (USS) to acquire the downlink control information. After obtaining the downlink control information, the terminal obtains the TBS according to a TBS table, and uses the TBS for demodulation and decoding.
There are a variety of radio network temporary identities, including Semi-Persistent Scheduling (SPS), Semi-Persistent Scheduling Cell RNTI (SPS C-RNTI), Cell RNTI (C-RNTI) etc. DCI formats related to the PDSCH include DCI format 1, DCI format 1A, DCI format 1B, DCI format 1C, DCI format 1D, DCI format 2, DCI format 2A, DCI format 2B, DCI format 2C, DCI format 2D etc.
For the uplink adaptive modulation and coding technique, the base station can acquire uplink channel parameters from a Sounding Reference Signal (SRS) transmitted by the UE and determine the MCS index and the resource allocation information for the uplink transmission of the UE based on the acquired channel parameters. Specifically, the Rel-8 LTE protocol defines a Modulation and TBS index table for a Physical Uplink Shared Channel (PUSCH), which may also be referred to as an uplink MCS table hereinafter. The base station transmits the MCS index and the resource allocation information through the downlink control information. The terminal can carry out the modulation and coding of the uplink data using the information and transmit the uplink data on a corresponding PUSCH resource. The DCI format associated with PUSCH includes DCI format 0, DCI format 3, DCI format 3A, and DCI format 4. It should be illustrated that the downlink MCS table and the uplink MCS table can be collectively referred to as a MCS table.
After LTE system has experienced several versions of Rel-8/9/10/11, research is continuously carried out on the R12 technology. In the existing Rel-11 standard, the uplink and the downlink support a modulation and coding scheme of at most 64 Quadrature Amplitude Modulation (QAM). With the development of heterogeneous networks, small cells need a higher data transmission rate and a higher system spectral efficiency, which requires the introduction of a higher-order modulation and coding scheme, such as 256 QAM. The existing standards cannot meet the requirements. For example, a conventional table of the existing LTE standard, i.e., the CQI table/MCS table/TBS table supports a modulation and coding scheme of at most 64 QAM and a spectral efficiency of about 5.5547 bit/s/Hz.
By taking the LTE system as an example, the above description shows that the conventional table (i.e., the existing CQI table, MCS table and TBS table) cannot support a higher-order modulation. After the introduction of a high-order modulation, such as 256 QAM and 1024QAM in the existing communication system, enhanced tables (new CQI, MCS and TBS tables) supporting the high-order modulation should be designed.
Currently, the conventional table of the communication system can neither support the higher-order modulation, nor can solve the problem of the specific configuration and usage of the enhanced table for the high-order modulation and the conventional table. Therefore, the communication system currently cannot support the higher-order modulation. In scenarios where the channel conditions are good and higher-order modulations may be applied, for example, in small cell scenarios, the improvement of the peak data transmission rate and the spectral efficiency of the system is limited.